The present disclosure relates to a thin film transistor and a method of producing the thin film transistor, and more specifically to a thin film transistor provided with a semiconductor layer containing a carbon nanotube and a method of producing the thin film transistor.
An active driving circuit provided with a thin film transistor (TFT) has heretofore been embedded in each of pixels of a bright and easy-to-view flexible display such as an organic EL, a film liquid crystal, and an electronic paper. Among TFTs, an organic TFT using an organic semiconductor can be produced at ordinary temperatures and is expected to be the one that can be formed on a flexible plastic substrate at a low cost. Meanwhile, the organic TFT has problems such as low carrier mobility and poor environmental stability.
As a countermeasure, there have been proposed a semiconductor element using as a semiconductor layer obtained by printing or applying a gel composition formed of a carbon nanotube and an ionic liquid on a substrate and a method of producing the semiconductor element (see Japanese Patent Application Laid-Open (JP-A) No. 2005-209736, for example). There has also been proposed a method of producing a field effect semiconductor device obtained by dispersing a carbon nanotube into a solvent such as ethanol or dimethylformamide and depositing and dry-fixing the carbon nanotube in a predetermined pattern (see JP-A-2005-93472, for example). According to the semiconductor elements and the production methods therefor disclosed in JP-A-2005-209736 and JP-A-2005-93472, it is possible to form a semiconductor layer having high mobility due to excellent material characteristics of the carbon nanotube such as high electron speed and high current density. Also, since the carbon nanotube has high flexibility and is a strong and thin threadlike material, the carbon nanotube is suitably used for flexible displays.
However, the semiconductor element and the production method therefor disclosed in JP-A-2005-209736 and the production method for the field effect semiconductor device disclosed in JP-A-2005-93472 have both of advantages and drawbacks. For example, according to the semiconductor element and the production method therefor disclosed in JP-A-2005-209736, since the gel composition containing the carbon nanotube and the ionic liquid is used in forming a semiconductor layer, there is an advantage that the semiconductor layer can be formed by a wet processing such as coating. Meanwhile, since the ionic liquid mentioned above is in the form of a gel, there is a drawback that the semiconductor layer cannot be formed by a simple coating process such as an inkjet method. Also, the production method for the field effect semiconductor device disclosed in JP-A-2005-93472 has an advantage that manufacturing by a simple method is possible. Meanwhile, since it is difficult to uniformly arrange the carbon nanotubes due to poor dispersibility of the carbon nanotubes, there is a drawback of a large variation in characteristics of the thin film transistors to be produced. In a microscopic device such as the flexible display, the variation in characteristics of the thin film transistor greatly influences on operation of the whole device. Therefore, there has been a strong demand for establishment of a method of producing a thin film transistor having stable transistor characteristics.